问题
单项选择题
You must（）in this area unless you have messages about the casualty.
A.keep radio silence
B.keep radio silent
C.keep radio be silent
D.keep silent the radio
答案
参考答案：B
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You must（）in this area unless you have messages about the casualty.
A.keep radio silence
B.keep radio silent
C.keep radio be silent
D.keep silent the radio
参考答案：B